When I look at "Other SSIDs" in the Air Marshal, all signal strengths are reported as positive values - probably because the unit of measure is dB, and not dBm. So, it is a ratio. A ratio to what? Why would I see 33 dB when I turn on the hotspot on my cell phone, and see -67dBm when reported by my UniFi dashboard?
I was asking on another forum about a neighbor who was showing up with 50+ devices at >90dB signal strength, hosing my own WiFi, and they insisted that it should be a non-issue because that is essentially zero. But, -90dBm would be essentially nothing - not positive 93dB as I see in the dashboard.